Are you similarly confused by the use of the plural "You" instead of the singular "Thou"?
I'm not, as the language has evolved.
Language is constantly evolving and shedding antiquated words in the proccess. There's no moral significance or utilitarian considerations to be drawn from this - it's simply the natural course of linguistic development. I work with Indians on a regular basis, and I can tell you that there are many phrases that they use or we use that are misunderstood despite the long-standing use of English in both of our countries - the both started in England, but each developed independently of each other and variations resulted. The same changes occur even within a country's own borders. I have well-educated friends in Texas that use the phrases might to could, and used to could, etc., and the first time I heard them, I had no idea what they meant as no one used these phrases in the Northwest, where I learned the language. What's important for him, is to know that outside of the South, the use of those phrases leads to confusion. There not "wrong" in a certain linguistic circle, but they are meaningless and confusing outside of that circle. It would ridiculous for him to obstinately assert that because it's understood by some that everyone should understand and accept the phrase. Ultimately, the person that loses is him as he handicaps his own ability to communicate. It's no different in this case.